In the following, the distal end of an injection device or drive mechanism is referred to as the end where a cartridge and e.g. a needle are located, whereas the opposite end is the proximal end. A dose button may be provided at the proximal end.
The general function of a drive mechanism as defined above is to set a dose and to subsequently dispense the set dose. Dose setting (dose dialling) usually requires a user to manipulate one element of the drive mechanism, preferably to rotate a dial member e.g. via a dial grip. During dose dispensing the dial member may move, e.g. rotate, back to its original position wherein a drive member, which is not actuated during dose setting is moved together with the dial member during dose dispensing. The movement of the drive member may be a rotation, a displacement in the distal direction or a combined movement e.g. along a helical path. The drive member may act on a piston rod, e.g. a lead screw, for expelling medicament from a cartridge during dose dispensing.
In addition to this basic function of a drive mechanism it is in some cases preferred to allow a resetting of an already set dose, i.e. a correction or a deselecting of a dose. Preferably the user simply has to rotate the dial member, e.g. via a dial grip, in the opposite direction compared to the rotation during dose setting. Preferably, the drive member is not actuated during dose resetting, either.
At the beginning of dose setting, the mechanism is usually in a zero dose position, i.e. the previous dose has been fully administered and no new dose has been dialed. The user may set a dose up to a maximum dose which is defined by the mechanism, for example by providing an end stop which prevents setting of a higher dose. Typically, a maximum settable dose is 60, 80, 100 or 120 units of a medicament. During dose resetting, an already set dose may be reduced down to the zero dose position of the device. It is important that a user fully dispenses the required set dose to avoid an underdose which may have serious medical consequences. Thus, it is required to indicate to a user that the mechanism is in its zero dose position after dose dispensing.
An injection device as defined above is known e.g. from EP 1 974 761 B1 wherein during dose setting, dose resetting and dose dispensing a dose grip and a dose dial sleeve rotate with respect to a housing and a housing insert between a zero dose position and a maximum dose position. A visual indication of the dose is provided by reference numerals on the outer surface of the dose dial sleeve. A window in the housing allows the visual indication of the dose currently dialed to be viewed.
In addition, a drive mechanism is known from EP 0 730 876 B1 which includes a housing and a dial. The dial is rotated during dose setting and axially displaced during dose dispensing. As the dial reaches its end of dose position (zero dose position), a finger of the dial moves past a housing edge and into a housing groove, which creates a click sound thereby providing an audible confirmation that the entire dosage has been injected. Further, WO 2006/079481 A1 discloses a similar mechanism, which provides a non-visual feedback signal to a user only at the end of injection of a set dose. This is achieved by providing two parts which perform a relative rotational movement during injection of a dose, wherein the two parts abut or engage thus causing the non-visual feedback signal. In some embodiments of WO 2006/079481 A1, the two parts may perform a relative rotation during dose setting, too. A relative rotation during dose resetting is not described. The mechanisms of EP 0 730 876 B1 and WO 2006/079481 A1 do not prevent that the click sound or non-visual feedback signal is generated during dose resetting. Thus, users may be confused if a signal is provided which indicates completion of the dose dispensing process even if the user did not initiate this dispensing process.
Further, WO 2011/060785 A1 discloses a scale with an end-of-dose ratchet arm. The scale rotates during dose setting, dose correction and dose dispensing. The housing comprises a stop rib which the ratchet arm passes just before the injection stops. This creates a clicking sound different from the sound of injection clicks. Further, scale is axially movable against the bias of flexible arms when the actuation button is pressed. The flexible arms displace the scale back after dose dispensing. This results in the end-of-dose ratchet arm not interfering with the stop rib during dose setting, i.e. when the actuation button is not depressed. A similar mechanism is known from WO 2011/060786 Al disclosing a dispense clicker mechanism having a series of teeth on an inner side of the housing with one tooth having a different configuration. A ratchet arm is held in a position not interfering with the teeth during dose setting or dose correction and is moved axially to a position engaging teeth during dispensing. Tooth is located such that a different click is generated at the end of injection.